The present invention relates generally to fasteners for plastic containers and, in particular, to a clip for attaching a component to a mounting surface of a plastic material container.
Plastic containers, such as automobile fuel tanks, are well known. Fuel tanks are part of the fuel system for the automobile and used for storing the liquid fuel, such as gasoline or diesel fuel, for the automobile""s internal combustion engine. Fuel tanks typically include components disposed therein including fuel delivery modules, fuel pumps, fuel filters, and various other components of the fuel system.
Most prior art plastic fuel tanks are constructed of plastic materials such as high density polyethylene (HDPE) and low density polyethylene (LDPE), among others, utilizing a blow-molding process. In the blow-molding process, the plastic material is extruded into a mold and then pressurized against the sides of the mold, forming the tank as a single, unitary body. These prior art plastic fuel tanks typically include a plurality of components such as wiring harnesses, vapor lines, and the like, attached to the exterior surface thereof. Traditionally, these components are attached to the blow-molded fuel tanks with clips using a costly and time-consuming process known in the art as a xe2x80x9chot plate weldingxe2x80x9d process. The hot plate welding process involves heating a surface of the clip, heating a portion of the exterior surface of the tank, and then placing the respective heated areas of the clip and tank in contact with one another to form a bond. After the clips are hot plate welded to the exterior surface of the tank, the components are then placed in the clips. Other alternatives to the hot plate welding process include the use of a spin welding process, an ultrasonic welding processes, or by creating a die lock in the molded tank. Creating a die lock, however, is generally difficult and occasionally impossible due to geometry constraints. In addition, the clips of the prior art are orientation specific in that the clips have a specific mounting surface that must be oriented towards the exterior surface of the container to which it is to be attached in order to be attached correctly. Any deviation in the mounting orientation of the clips can result in an inadequate bond.
Moreover, regulatory changes affecting evaporative emissions have driven fuel tank designs to internalize the components that traditionally have been welded to the outside surface of plastic fuel tanks, such as valves and vapor lines because these each of these external component connections are a potential evaporative emissions source. Hot weld points that penetrate the tank permeation barrier, in particular, are noted sources of evaporative loss. Attaching components to the interior surface of blow-molded tanks is difficult without first creating a large opening in the tank and then placing the components in the interior of the tank. The large opening is an additional evaporative emissions source, which defeats the purpose of minimizing evaporative emissions from the tank. Components are also placed inside tanks on rods, which results in a hole in the side of the tank that must be sealed. More recently, fuel tanks have been manufactured with a process known as thermoforming, which provides for additional configurations for fuel tanks because the tank is formed in two halves having opposing planar attachment faces that are then joined together. Because the tank is formed in halves, this presents an opportunity to locate components inside the fuel tank that previously have been located on the exterior of the tank.
It is desirable to attach components to a surface of a plastic container without the use of hot plate welding in order to reduce the overall cost of the containers. It is also desirable to attach components to the interior surface of plastic containers without regard to the orientation of the clips. It is desirable to reduce the amount of evaporative emissions emanating from fuel tanks.
The present invention concerns a clip for attaching a component to a mounting surface constructed of a plastic material. The clip includes a preferably tubular clip body of any suitable shape having a central aperture defined by an interior surface and an exterior surface. A plurality of projections are formed on and extend radially outwardly from the exterior surface. The projections can be in the shape of barbs, ridges, teeth, dimples, small hemispheres, or the like. A gap extends through a wall of the clip body between the interior and exterior surfaces and has a width insufficient to pass the component. In one embodiment, the gap extends between opposite ends of the clip body generally parallel to a longitudinal axis. Alternatively, the gap is helical in shape extending around the clip body between the opposite ends. Regardless of its shape, the clip body wall can be deflected outwardly to widen the gap for receiving the component in the central aperture. When the deflecting force is removed, the clip returns to the original shape and the component is securely retained.
The clip body is preferably constructed of high density polyethylene (HDPE), low density polyethylene (LDPE), or the like. The clip body is adapted to receive a component, such as a fuel vapor line or wiring harness, in the central aperture and to adhere to a mounting surface, such as the interior or the exterior surface of a thermoformed fuel tank, without the aid of unique assembly fixtures or pre-heating of the clip.
The clip body adheres to the mounting surface because when placed against the mounting surface, such as during the thermoforming process of a plastic fuel tank, the contacting projections are melted by the latent heat of the recently formed mounting surface. The mounting surface is preferably constructed of HDPE or LDPE material having a melt index slightly lower than the melt index of HDPE or LDPE material of the clip body. If the melt index is lower, the polymer is more viscous. More importantly, the mounting surface has a much greater thermal mass in comparison to the clip body. Because of the large difference in the respective thermal masses of the mounting surface and the clip body and because of the difference in the melt indexes of the mounting surface and the clip body, the latent thermal mass of the plastic material of the mounting surface transfers enough heat into the clip fins to melt the clip fins to create a bond between the mounting surface and the clip body. Thus, the clip welds immediately to the mounting surface when the projections contact the mounting surface. The wall thickness of the clip body acts advantageously as an insulating barrier, stopping the weld process when the projections have melted to the weld area.
The present invention is adaptable to be installed on the component during the component manufacturing process, minimizing the burden when the component is later assembled with the mounting surface. The clip is advantageously not orientation-specific in that the clip may be welded in 360-degree orientation around the longitudinal axis of the clip body with no change in function, minimizing the need for any additional processing of the clip once it is placed on the component.
The clip is preferably manufactured by an injection molding process. Alternatively, this clip may be formed in a simple multi-cavity open-close mold having minimal dimensional requirements. The clip also may be manufactured using a continuous extrusion process, where the axial shape of the clip is extruded, then cut to length and slit along a helical angle, the helical slit being such as to increase the likelihood of a weld bond across the clip opening.
The present invention recognizes that thermoforming and processes that support internalization of components allow the opportunity to create a new type of clip that advantageously does not require specialized tools or processes for installation. The clip according to the present invention is simply pressed against a mounting surface having a latent heat and it automatically welds to the mounting surface. The present invention recognizes that by utilizing the latent heat at a mounting surface of a thermoformed plastic material, a clip formed of a similar plastic material can be welded to the mounting surface by utilizing different thermal masses.
The clip of the present invention may be used advantageously with HDPE and LDPE fuel tanks. In addition, those skilled in the art will appreciate that this type of clip may be used for attaching many types and shapes of components to various mounting surfaces constructed of plastic or similar materials.